Direct viewing storage tube



Nov. 27, 1962 v. .1. LEGENDRE 3,066,234

DIRECT VIEWING STORAGE TUBE Filed March 5, 1959 [/7 Men 2170;". Mata/"f4 & fiend/"8 trite This invention relates generally to charge storage tubes of the direct viewing, i.e., signal to-image variety, and more particularly to the image section of such tubes.

Direct viewing charge storage tubes are well known in the art, conventionally comprising an enclosing envelope with a phosphor display screen at one end and with high velocity writing and low velocity flood electron guns at the other end. An image screen assembly is disposed within the envelope adjacent the phosphor display screen, this assembly commonly including a fine mesh screen of dielectric material having secondary emission properties with a metal backing layer on one side thereof, commonly referred to as an insulator or charge storage screen, and a fine mesh metal collector screen closely spaced from the dielectric side of the storage screen and facing the electron guns. In the conventional operation of such signal-toimage storage tubes, a high velocity pencil electron beam is caused to scan the storage screen assembly by means of conventional deflection and focusing elements, the high velocity electron beam impinging upon the dielectric coating on the storage screen thereby displacing secondary electrons which are collected by the collector screen leaving a charge on the storage screen caused by the deficiency in electrons thereon; by modulating the high velocity electron beam in accordance with an incoming signal, the discrete areas of the storage screen defined by the openings therein will have different charges thereon thereby forming a pattern or charge image on the storage screen corresponding to the input signal. This charge image is retained on the storage screen for a substantial period of time and may be read-out at any time during its existence by flooding the storage screen with a flood beam of low velocity electrons from the flood electron gun; these low velocity flood electrons pass through the openings in the storage screen in accordance with the elemental charges thereon, and thus excite the phosphor display screen to provide a visible display of the charge image stored on the storage screen.

Since the image screen assembly has a diameter generally coextensive with the diameter of the phosphor display screen, direct viewing storage tubes cannot employ an envelope of the type used in conventional cathode ray tubes, i.e., open only at its neck portion to permit insertion of the electron gun and deflection elements, it being necessary at some stage during assembly of the tube to provide access to the enlarged portion of the envelope adjacent the display screen for positioning and securing the image screen assembly. Thus, in a common form of direct viewing storage tube construction, an all-glass en- .velope is used, the display screen and image screen assembly being initially disposed in what amounts to a glass beaker. In assembling a tube of this type, the phosphor is first deposited on the bottom of the beaker and is then aluminized to form the display screen. The image screen structure is then mounted, conventionally by spot welding the assembly to metal studs sealed in the side Wall of the beaker; this spot welding operation subjects both the pho phor display screen and the image screens to potential damage from heat, splashing of molten metal, and/ or touching, and once the screen structure is i in place, the phosphor display screen is diflicult to inspect. The neck section of the tube, including the electron gun and deflecting elements is then sealed to the image section with a conventional glass seal and the necessary conductive wall coatings are then applied. It will .be

rates dfttf ice understood that in such prior all-glass constructions, operations are performed subsequently to the formation of the phosphor display screen and the mounting of the image screens which may potentially cause damage to either or both of these elements and it will further be observed that the operations involved in mounting the image screens in the envelope are performed in what amounts to a deep Well.

Direct viewing storage tubes are quite costly and it is therefore sometimes desirable to rebuild the tube, which generally involves the repair or replacement of the image screens, which, by virtue of their fine mesh, are extremely fragile. In the prior all-glass tube constructions, however, rebuilding the tube required separation of the two envelope halves at the original sealing line with removal of the image screens still being diflicult by virtue of their being spot welded to the mounting studs and the fact that they were positioned in a deep well, i.e., adjacent the display screen. It is therefore desirable to provide a direct viewing storage tube construction in which the image screen assembly is more readily positioned and mounted within the envelope than has previously been the case and in which the sources of potential damage to the image screens and to the phosphor display screen which have previously existed being eliminated. It is further desirable that such an image screen mounting arrangernent permit ready removal of the screens for repair and replacement. In accordance with my invention, therefore, I provide an image screen assembly mounting construction which does not require the use of spot welding techniques nor the intricate insulating arrangements previously employed. Further in accordance with my invention, I provide a detachable face plate so that the image screen assembly is initially positioned and secured in place in the open end of the envelope prior to assembly and attachment of the face plate thereon. With this construction, therefore, the phosphor is deposited on the face plate and aluminized prior to attachment of the face plate to the envelope with the conductive coatings being applied to the inner wall of the envelope and the electron guns sealed in place in the neck portion thereof prior to assembly of the image screens therein. It will be observed that with this construction, the image screens are anchored in place very close to the open end of the tube so that there is very little depth to negotiate. In my improved construction, the face plate is assembled on the envelope by means of metal flanges respectively sealed to the open end of the envelope and to the face plate, these flanges being welded together at their outer extremities, thereby permitting several rebuildings of the tube merely by cutting away the Welded portion of the flanges, and, after rebuilding, the face plate may then be reassembled in place and the flanges rewelded.

A further requirement of direct viewing storage tubes is that the face plate be flush, i.e., in the same plane with the panel in Which the tube is mounted; if the face plate is deeply recessed, as has been the case in certain prior constructions known to the present applicant, a decided optical disadvantage is presented since it is necessary to view the phosphor screen directly from in front and in addition, it has not been possible to apply devices directly to the face plate of the tube. In accordance with my invention, therefore, I have arranged the face plate mounting so that the outer surface of the face plate is not recessed.

More particularly, I have provided a direct viewing storage tube having an image section comprising a glass envelope open at one end. A first metal ring has its inner portion sealed to the open end of the envelope and has its outer portion extending radially outward beyond the outer periphery of the envelope. A second metal ring is provided having its inner portion sealed to the face plate and having its outer portion extending radially outward therefrom, the first and second rings having their outer portions respectively abutting and joined by an integral connection so that the face plate closes the open end of the envelope with the phosphor screen facing inwardly. In order to provide for ready insertion and removal of the image screen assembly, a third metal ring is sealed in the envelope Wall spaced from the face plate and at least a pair of spaced stud members are secured to the third ring and extend axially therefrom. The fine mesh collector and storage screens are respectively provided with apertures formed therein with the stud members respectively extending therethrough thereby supporting the screens and insulators are provided on the stud members respectively spacing the screens and mutually insulating the same.

It is accordingly an object of my invention to provide an improved image section assembly for a direct viewing charge storage tube.

Another object of my invention is to provide an improved detachable face plate construction for a direct viewing charge storage tube.

A further object of my invention is to provide an improved detachable image screen assembly for a direct viewing charge storage tube.

Theabove-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

The single FIGURE of the drawing is a cross-sectional view of a direct viewing storage tube incorporating the improved image section of my invention.

Referring now to the drawing, my improved direct viewing storage tube construction, generally identified as 10, comprises a glass envelope 11 having an enlarged portion 12 open at one end with neck portions 13 and 14 extending from the other end. A conventional high velocity writing gun 15 is sealed in the neck portion 13 and a conventional low velocity flood gun 16 is likewise sealed in the neck portion 14. It will now be readily understood that conventional electron gun constructions, well known to those skilled in the art are employed, the specific electron gun constructions not forming a part of my invention. It will further be readily understood that the defleeting elements required for deflecting the high velocity electron writing beam from the electron gun 15 are not shown.

In accordance with my invention, I provide a detachable annular glass face plate 17 which closes the open end of the cylindrical envelope portion 12. Glass face plate 17, which has a suitable phosphor coating 18 deposited on its inner surface, is mounted in the open end of envelope portion 12 by means of a pair of matching rings 19 and 20. The first ring 19 includes an inner tubular or flange portion 22 sealed in the edge 23 of the open end of the envelope portion 12 by what is referred to as a housekeeper seal. A radially outwardly extending annular portion 24 is joined to the outer edge ,of the inner tubular portion 22. A-tubular portion 25 is provided having its inner edge joined to the outer edge of the annular portion 24 and having its outer edge joined to the inner edge of an annular flange portion 26*. The second metal ring 20 has an inner annular portion 27 sealed to the inner side of the face plate 17 in a mating recess, as shown. The outer portion of ring 20 extends radially outwardly conforming to and abutting the first ring 19 as shown, with the outer edges of the annular flange portion 26 and the outer portion 28 of the first and the second rings 19 and 20 being integrally joined at 29, as by a heliarc weld. It will be observed at this point that the outer side 30 of face plate 17 is disposed in a plane slightly outwardly from the plane of the outer portion 28 of mounting ring 20. Since the metal rings 19 and 20 are at the same potential as the phosphor display screen 18, e.g., 15,000

bk volts, a ring 32 of suitable insulating material, such as one of the potting materials well known in the art, is 'provided surrounding metal rings 19 and 20 engaging the adjacent outer periphery of the envelope portion 12 and the peripheral edge of face plate 17, as shown. It will be here observed that the outer axial face 33 of the insulating ring 32 is flush with the outer side 30 of the face plate 17.

It will now be seen that the phosphor layer 18 may be deposited on the face plate 17 and aluminized prior to assembly and attachment of the face plate 17 to the envelope portion 12, and it will further be seen that the conventional conductive coating 34 on the envelope portion 12 may be applied to the inner wall thereof and the electron guns 15 and 16 sealed in the neck portions 13 and 14 respectively prior to positioning and attachment of the image screen assembly 35 and attachment of the face plate 17. It will further be observed that the face plate 17 may be readily removed for removal and subsequent replacement of the image screen assembly 35 merely by removing the insulating ring 32 and cutting away the welded portion of the rings 19 and 20; after rebuilding of the tube, the face plate 17 can be reassembled in place and the rings 19 and 20 welded together again, followed by forming of a new insulating ring 32 therearound.

The image screen assembly 35 includes a fine mesh metal collector screen 36 and a fine mesh insulator or storage screen 37, the latter conventionally being formed of a fine mesh dielectric screen facing the collector screen 36 and having a conductive coating on its side facing display screen 18. The collector and insulator screens 36 and 37 must be insulated one from the other since they have different potentials applied thereto and they further must be anchored securely within the envelope portion 12. In order to provide for ready initial attachment and subsequent removal of the image screen assembly 35, the arrangement now to be described is provided. An annular metal ring 33 is provided in the envelope portion 12 and sealed to the inner Wall thereof, as shown, ring 38 being spaced inwardly from face plate 17. A plurality of spaced apart stud members 39 are provided secured to the ring 38 and extending axially therefrom toward face plate 17. Stud members 39 are shown as being secured to ring 38 by being threadingly inserted in appropriately tapped openings in the ring 38. The fine mesh collector screen 36 is mounted on a suitable metal support ring 40, the collector screen 36 and support ring 40 being provided with a plurality of apertures therein through which stud members 39 respectively extend thereby supporting collector screen 36 in abutment with the annular mounting ring 38. A pair of ceramic spacing Washers 42 and 43 are respectively positioned on each of the stud members 39 and the insulator screen 37 with its support ring 44 are likewise provided with a plurality of apertures formed therein corresponding to the stud members 39. In order, however, to insulate the insulator screen 37 from studs 39 which are at the same potential as the collector screen 36 and the mounting ring 38, the apertures in the insulator screen 37 and its mounting ring 44 are larger than the studs 39 with ceramic washers 43 having portions respectively extending into the apertures 45 thereby insulating the insulator screen and its support ring 44 from the studs. Collector screen 36 and insulator screen 37 are held in assembled relation with ceramic washers 42 and 43 providing the requisite insulating spacing therebetween by means of insulating washers 46 on the studs 39 in abutment with the support ring 44 and suitable nuts 47 threaded onto threaded ends 48 of studs 39.

It will now be readily seen that my improved image screen assembly mounting arrangement completely eliminates the spot or resistance welding previously employed in attaching image screen assemblies with the consequent potential damage to the fine mesh screens by hot metal splashes and touching. It will further be seen that extremely small spacing may be provided between the two screens. Lastly, and importantly, it will be observed that the screens 36 and 37 may be readily removed, following removal of the face plate 17 as previously described, merely by removing the nuts 47 from the threaded ends 48 of the studs 39. It will be readily comprehended that a threaded ceramic stud could be employed for mutually supporting screens 36 and 37 from the mounting ring 38, or that a conventional miniature bolt could be used instead of the stud members 39. It will thus be seen that in my improved image section construction for a direct viewing storage tube, not only is the face plate detachable permitting ready assembly and disassembly of the image screen assembly, but further, my improved image screen mounting arrangement completely eliminates the integral spot welded metal tabs and ceramic sleeves previously employed for anchoring the screens.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of my invention.

What is claimed is: In a direct viewing storage tube having a glass envelope with a cylindrical portion open at one end, a detachable face plate construction for said tube comprising a first metal ring having a first tubular portion sealed to the edge portion of the open end of said envelope and having an annular portion extending radially outwardly therefrom; a glass face plate for said tube and a phosphor coating on the inner face thereof, said inner face being aligned substantially transversely with the edge of said envelope, a second metal ring having an annular inner portion sealed to said inner face of said face plate and in contact with said coating, and an outer portion extending radially outwardly from the peripheral edge of said face plate and abutting said first ring, the outer edges of said first and second rings forming a common rim and being sealed together by an integral peripheral connection closing the open end of said envelope, the outer face of said face plate extending forwardly from said tube beyond the outermost portions of said rings; and an annular ring of removable insulating material enclosing said first and second rings and engaging the peripheral surface of said envelope and the edge portion of said face plate, the forward outer face of said insulating material being disposed flush with the outer face of said face plate. 

